With a budget of $175 million, the 91.5m (300ft)-high stand, to be the agency's tallest at the Stennis Space Center, is to be located in what is currently a heavily forested greenfield site.

As well as the test stand the facility consists of propellant barge docks, a test control centre, engine and stage-handling systems, fire detection and water deluge systems and a support personnel building.

The stand will be able to test engines with up to 1,000,000lb thrust (4,450kN) and gimbal powerplants in a 5e_SDgr square pattern. The Apollo programme's Saturn V rocket's F-1 engine had 1,500,000lb thrust.

"The stand will test fire its first J-2X in December 2010. But test stand trials begin in August of that year," says Stennis's A-3 project manager Lonnie Dutreix.

For the testing programme the facility will be able to store 625,000 litres (165,000USgal) of liquid oxygen (LOX) and 492,000 litres of liquid hydrogen (LH2).

But of the 625,000 litres of LOX, only 227,000 is to fuel the engine, the other 397,000 is used to generate the vacuum necessary to simulate a near-space altitude of 100,000ft.

The remaining 720,000 litres of LH2 and LOX will provide sufficient propellant to enable engine pre-chilling, a full flight profile test and long duration, 550s, testing.

In late August Stennis's A-1 test stand, previously used for testing Space Shuttle main engines, will test the J-2X's turbomachinery.

But the A-1 began life testing the Saturn V's J-2 engine, the J-2X's antecedent.